Rainwater Collection Tank Calculator

For every 1 inch of rain on 1,000 sq ft of roof, you can collect about 600 gallons (accounting for losses). A 1,500 sq ft roof in an area with 40 inches of annual rainfall can collect roughly 30,000-35,000 gallons per year.

For garden irrigation only, a 500-1,000 gallon tank is typical. For landscape use, 1,000-2,500 gallons. For whole-house non-potable use, 5,000-10,000 gallons. Size depends on your dry season length and daily usage.

Raw rooftop rainwater is not safe to drink without treatment. It can contain bacteria, chemicals from roofing materials, and debris. With proper filtration (sediment + carbon), UV treatment, and possibly reverse osmosis, it can be made potable. Always test water quality.